Observation of 3-D Birefringence Distribution of Polymer Thin Film by Near-Field Optical Microscope

According to development of optical engineering, the measurement accuracy of optical components and materials has become more important. For example, birefringence in polymer thin film is an essential issue for development of liquid crystal display. In this study, after a PVA (poly vinyl alcohol) film was embedded by photopolymer and cut by ultramicrotome, a cross-sectional birefringence distribution of cut film was observed by birefringence contrast scanning near-field optical microscopy (B-SNOM). As a result, three dimensional birefringence ratios were calculated and birefringence of parallel to stretching direction was larger than that of vertical one. This result shows that cross-sectional birefringence distribution is yielded by inhomogeneous distribution of molecular alignment in film material according to asymmetry stretching.